Process of dehydrogenation



Patented Dec. 29, 1953 STAE TNT OFFICE PROCESS OF DEHYDROGENATIONDelaware N Drawing.

Application Gctober 24, 1949, Serial No. 123,301

18 Claims. (Cl. 260-680) This invention relates to an improved method ofdehydrogenating hydrocarbons. For example parafiins may bedehydrogenated to the corresponding olefins, usually in admixture with asmall proportion of the corresponding diolefin.

Or olefins may be dehydrogenated to the corresponding diolefins, usuallyconjugated. Thus the y catalyst of the present invention is particularlyapplicable to effect the conversion of normal butane to a mixture ofnormal butenes and butadi ene, but it is also effective in theconversion of cyclohexane to cyclohexenes and benzene, n-heptane totoluene, etc. For such a conversion the catalyst is preferably promotedwith chromic oxide (ClzOs, also known as chromium sesquioxide or aschromia). The alumina catalyst of the present invention is also verysuitable for eifectlng the conversion ofnormal butenes to butadiene,especially when a minor proportion of magnesia is incorporated as apromoter during its manufacture.

This application is a continuation-in-part of my copending applicationSerial No. 634,767, filed December 13, 1945, now Patent No. 2,499,675.

, The principal object of the present invention is to provide animproved process for dehydrogenation of hydrocarbons, particularlyparafiins to olefins and/or diolefins, and of olefins to diolefins.Other objects of the invention will become apparent from theaccompanying disclosure.

It is known that, in the preparation of activated alumina by dehydrationof such materials as precipitated alumina gel and from minerals such asbauxite and gibbsite, the activity of the dehydrated alumina depends onproper control of the dehydration temperature. For example, aluminaprepared by dehydrating bauxite at about 1000 F. is an active catalystfor dehydration, dehalogenation, dehydrogenation, etc., whereasanhydrous alumina prepared by dehydrating hydrous alumina above 2200 F.is comparatively inactive catalytically. Although the effect ofdehydration temperature on activity of dehydrated alumina is notcompletely understood, it is believed that treatment at or above 2200"F. efiects an intermolecular rearrangement theresult of which is a formof alumina having a relatively low surface area per unit Weight.

Commercially available activated alumina is often prepared bydehydrating minerals such as bauxite and gibbsite at about 1000 F. Forexample, alumina trihydrate is calcined to a moisture content of 8 to 10per cent and then compressed into pellets, and the pellets are calcinedto re move the balance of the combined water.

Pelleted activated alumina prepared in this manner has a surface area ofabout to square meters per gram, measured by gas adsorption at lowtemperatures. In practice, the preparation process is usually notclosely controlled; the chief control criterion is the suitability ofthe activated alumina for the intended use.

I have now found that a markedly superior alumina catalyst may beprepared by the steps of (l) calcining hydrated alumina containing atleast 28 per cent by weight of combined water under conditions such thatit is only partially dehydrated,'namely to an extent such that thecalcined material contains between 20 and 26 per cent of combined water,(-2) compressing the resulting finely-divided material into pellets and(3) calcining the resulting pellets at a high temperature and under suchconditions as to remove the residual combined Water or water ofhydration.

Raw material for catalyst preparation As the raw material for themanufacture of the catalyst of the present invention, I may use anysuitable formof hydrated alumina containing 28 per cent by weight ormore of combined water. The preferred raw material for making thecatalyst of the present invention is that form of alumina trihydratewhich is formed as a byproduct in the Bayer or Flakes-Sherwin processfor the precipitation of alumina from alkali aluminate aqueous solution.This material is formed as a scale on the precipitating tanks. It isobtainable from the Aluminum Company of America and is the raw materialused in the manufacture of Activated Alumina. For a more detaileddescription of this material, attention is directed to U. S. Patents toBarnitt 1,868,869 and Derr 2,015,593. This material has the chemicalformula A12O3.3I-I2O and is very pure. It may be termed an artificialgibbsite.

Less desirably, I may employ naturally occurring materials such as thosevarities of bauxite or gibbsite which contain combined water in theneighborhood of 28 to 35 per cent. Generally speaking such naturalaluminas are believed to be of the trihydrate type, that is to contain amajor proportion of alumina trihydrate, A12O3.3H2O. However, it is to beunderstood that the invention is not to be limited by any theoreticalconsiderations and the principal criterion as to the suitability of theraw alumina is that it contain 28 per cent or more by Weight of combinedwater. This figure is of courseindependent of any free water which canbe removed readily by simple drying at say 220 F.

While I prefer to use alumina trihydrate obtained as a by-product in themanufacture of metallic aluminum, and may somewhat less desirably usenaturally occurring alumina trihydrate such as bauxite or gibbsitecontaining 28 per cent or more of combined water, I do not wish toexclude from the present invention the use of synthetically preparedalumina trihydrate pree pared for example by precipitation of aluminagel followed by drying to the trihydrate.

Whether by-product, natural or synthetically prepared, the hydratedalumina employed as raw material in carrying out the present inventionis preferably in granular form. In size it may range from 100 mesh up tolumps as large as e to inches. As received from the Aluminum Company ofAmerica, by-product alumina trihydrate formed as scale in precipitationtanks was of i0 to 100 mesh in size of particles. Apparently it has beenground prior 'to shipment. The size of the original material isnotpa-rticularly critical as long as it is not so large that dehydrationis not uniform due to dimculty of removing liberated water or to poorheat penetration into the interior of the granules during the relativelyshort partial dehydration step.

Partialdehydmtion step In the first step of making the catalyst, thehydrated alumina is heated under conditions controlled to producepartially dehydrated alumina which, when ignited to constant weight atabout 2200 F., undergoes a weight loss of 20 to 26 per cent. In otherwords, the calcination is so controlled that the resulting materialretains between 20 and 26 per cent of combined water. Since the weightlosson ignition is the chief control criterion in this step, the partialdehydration procedure may vary somewhat in different'specificembodiments of the invention. It is preferred to conduct this step at atemperature of about 480 .F. A temperature as low as 470 F. ranging toas high as '4l 90 F. may be employed in thisstep. Rather. closetemperature control during this step is important since temperaturerather than time is the principal factor in determining the extent ofwater removal. However, it will be unde stood that other conditionsincluding time are so ad usted that combined water is removed only totheextent specified.

Provision should be made for removing the water liberated during thepartial dehydration step. If desired, the moisture may be removed assoon as formed by passing a current of gas over or through the materialundergoing calcination. The natural draft in an ordinary rotary kiln isoften adequate for th s purpose.

In the case of by-product alumina trihydrate formed as scaly deposit inthe precipitation tank where alumina is precipitated from alkalialuminate solution, a preferred procedure comprises heating the materialin a gas-fired rotary kiln at about 4:80 F.

While I do not wish to be limited by theoretical considerations,nevertheless it may be that the partial dehydration step serves toremove one molecule of combined water from the alumina trihydratepresent in the starting material, thereby convertingthealuminatrihydrate content of the initial materialtothe dihydrate form. It will"be understood that the original alumina trihydrate may contain a m norproportion of impurities so that evenafterdryiug to remove any freewater it may not be per cent pure alumina trihydrate. This may serve toexplain why the partially dehydrated material may contain as low as 20per cent of combined water Whereas pure alumina dihydrate, AlzOs-ZHzO,would contain 26 per cent by weight of combined water. However, it is tobe understood that the present specification fully discloses the actualsteps employed in the practice of the present invention and accordinglythat the invention is not dependent upon the accuracy of the foregoingspeculations. For instance, the existence of a compound having theformula A12O3-2H2O is subject to some doubt. Regardless of whether thecompound alumina dihydrate ex sts or not, I have discovered that thesteps outlined herein produce the results described and have givendetails sufficient to enable those skilled in the art to practice theinvention.

Following the partial dehydrating step, the material is allowed to coolin any suitable way and is now ready for the second step. The coolingmay be efiected in any usual way, for example, by allowing it to standin any suitable atmosphere until its heat has been dissipated. Thecooling should be carried out in such a way that re-hydration of thematerial does not occur. Ordinary cooling does not cause suchrehydration.

Pelleting step In the second step of the catalyst preparation thepartially dehydrated alumina is compressed into pellets. This operationis well known and need not be described in detail. It is variously knownas pilling, pelletng, or tableting. In essence it amounts to subjectinga suitable mass of powdered material to such high pressure that itretains its shape after release of the pressure and discharge from thepilling machine. Pills or pellets of any desired shape or size can bemanufactured. Usually, however, the pills are not larger than inch by Ainch.

Final calcz'nation The pelleted alumina is then calcined underconditions such that the residual combined water is removed. While thismay be done in any suitable way, I find it preferable to conduct thisoperation at a temperature ranging from 900 F. to 1200 F. In exceptionalcases a temperature as high as 1300 F. may be employed, but results arenot as satisfactory as when a temperature not over 1200 F. is employed.Temperature ranging from 1200 F. to 1300 F. injure the catalyticactivity of the material and preferably are avoided. Temperatures above1300" F. are even more injurious and are never employed.

In a typical and preferred embodiment the pelets are calcined at about1000 FE, other conditions being such that the residual combined water iscompletely removed.

Pelleted alumina product Pelleted alumina made in the foregoing manneris characterized by superior properties. It has a surface area of theorder of 250 square meters per gram which is about twice that ofactivated alumina pellets hitherto commercially available which are madeby dehydrating the and possibly for other reasons not yet known withcertainty, pelleted alumina prepared in accordance with the process ofthe present invention is a superior catalyst, especially for thedehydrogenation of parafiins to the corresponding olefins and/ordiolefins.

Alumina prepared in accordance with the present invention may beemployed either directly as a catalyst or as a catalyst ingredient withimproved results. Thus a promoter for the alumina may be incorporated inany suitable way during manufacture of the pelleted alumina. Or thefinished pellets may even be impregnated with a promoter or a compoundconvertible to a promoter. If desired other catalytic materials ormaterials convertible to catalysts may be incorporated duringpreparation of the pellets or even after preparation. Thus aluminaprepared according to the principles of the present invention may beemployed as a catalyst support.

Although activated alumina prepared in accordance with this invention isespecially, desirable as a dehydrogenation catalyst or as a component ofa dehydrogenation catalyst, it is not limited thereto but may be usedwherever activated alumina catalysts have been used heretofore. Thus itmay be employed as a catalyst or catalyst ingredient for cracking,dehydration, polymerization, dehalogenation, cyclization and for anyother catalytic processes Where a superior activated alumina catalyst orcatalyst component is desirable.

Grinding step In many cases the partially dehydrated material is groundbefore the pelleting step. This may be conducted in any suitable mannerand equipment, for example in a ball mill. It is preferably a finegrinding operation. The grinding is carried out dry, that is without theaddition of water. Provision may be made for recycling coarse particlesto the grinding step for further grinding. The material leaving thegrinding zone may be used directly in the pelleting step or may besieved to any desired size, oversized particles being returned.

The extent of particle size reduction in the grinding step is variablewithin wide limits and depends primarily upon the particle size of theoriginal material, the duration of the grinding and the particle sizedesired in the product. Purely as an example, where 40 to 100 meshby-product alumina trihydrate obtained from the Aluminum Company ofAmerica is used as the original material, the partially dehydratedmaterial may be ground to an extent such that approximately onethirdpasses through a 300-mesh sieve. The material may be ground to any othersuitable fineness such as 90 per cent through a ZOO-mesh sieve or 90 percent through a 325-mesh screen.

Grinding and pelletz'ng lubricant cilitating the pilling step, it may beadded at any time sufiiciently prior to the end of the grinding stepthat intimate incorporation is effected When the lubricant is employedto facilitate the grinding step, it is preferably added ahead of thegrinding step or in the early portion of this step. Examples of suitablelubricants are graphite,hydrogenated oils such as hydrogenated corn oil,peanut oil, cottonseed oil, and the like, soaps such as aluminumstearate, etc., resins which may be natural or synthetic such as rosin,hydrogenated rosin, ester gum, polymerized rosin, etc. It is preferredto employ a lubricant which is destroyed during the calcination of thepellets. An advantage of organic compounds as lubricants is that theyinitiate binding forces upon calcination of the pilled or tabletedmaterial and thus impart strength to the finished catalyst so thatbreakage and dusting are minimized. Also the lubricant speeds up thegrinding and pilling steps and prevents unduly rapid wear of theequipment employed for these steps. The amount of lubricant employed mayvary from a trace up to approximately 10 weight per cent of the materialbeing ground.

Use of promoter It is often preferred to incorporate a promoter for thealumina during preparation of the pelleted alumina catalyst. A drypowdered promoter, or compound yielding a promoter upon finalcalcination, may be added before or during the grinding step asdisclosed in my copending application Serial No. 607,884, filed July 30,1945. Such a material may be admixed with the ground partiallydehydrated alumina priorto the pelleting. For example, a promoter oxidesuch as chromic oxide and/or magnesia may be incorporated with thealumina prior to pelleting. Other promoters or compounds forming sameupon calcination may be employed, such as magnesium hydroxide orcarbonate, or beryllium oxide. hydroxide or carbonate. Other catalyticcompounds or elements which may not function as promoters but rather astrue catalysts may similarly be incorporated. These include metals andmetal compounds as well as non-metallic catalysts, such as silica.

Alternatively, the pellets of alumina may be impregnated with a solutionof a promoter such as an aqueous solution of chromium trioxide, or witha solution of any other substance desired to be incorporated in thefinished catalyst. Upon calcination of the pellets in the third step ofmy process to remove the residual combined water, any water derived fromthe impregnating solution is removed and at the same time the chromiumtrioxide or other compound is converted to the form desired in thefinished catalyst.

General with the result that the resulting pellets have much greatersurface area-than do pellets prepared by dehydration of alumina to alower moisture content, then pilling, and then calcining to remove theresidual water. This is by no means a complete explanation. Although itis the best explanation now known to me, it does not serve to explainwhy calcination to a combined water content of between 20 and 26-weightper cent is critical. 'It is. to be understood that the invention is notlimited by any such explanation.

Dehydrogenation process Catalysts of the invention are particularly ad=vantageous in the-dehydrogenation of hydrocarbons. While the alumina maybe utilized without the incorporation of other dehydrogenating catalyststherein, composites containing one or more additional dehydrogenatingcatalysts are desirable in many instances. Metaloxides known to havedehydrogenating activity include the oxides of Cr, Mo, U, W, V, Mn, Zr,Th, Ti, Be, Mg, and Cu. Some of the metals themselves function desirablyin the dehydrogenation of hydrocarbons. The oxides oi the metals ofgroup VI (left-hand column) and of vanadium are particularly effective,either singly or in admixture, in aluminametal oxide composites.Coprecipitated aluminametal oxide composites, partially dehydrated andpilled by the method of the invention, are excellent catalysts fordehydrogenating hydrocarbons. The amount of metal oxide incorporated inthe composite may vary from 0.5 to '75 weight per cent based upon theweight of the composite but an amount in the range of 2 to 30 weight percent is preferred.

The conditions of the dehydrogenation, namely, temperature, pressure,contact time and space velocity, are those commonly used in the art.These conditions do not per se form a part of my invention. Accordingly,it is unnecessary to detail conditions here. The dehydrogenation of myinvention proceeds in the same general manner as in the prior art exceptwith higher production of the desired product, greater efdcicncy, andgreater retention of catalytic activity. The usual cycle of onstreamoperation followed by conventional regeneration for approximately anequal period is employed.

EXAMPLES Following are non-limiting specific examples of the practice ofthe in ention. In Example 11 the surface areas were measured by thelow-ternperature gas adsorption method of Brunauer, Emmett'and Teller,as described for example in J. A. C. S. 60, 309 (1938).

EXAMPLE I Granular alumina trihydrate as received from the AluminumCompany of America, made as a by-product in the manufacture of metallicaluminum having a size or" so to 160 mesh, was partially dehydrated byheating in a gas'fired rotary kiln. A weighed sample of the partiallydehydrated material when ignited to constant weight at about 2200underwent a weight loss of approximately 23 per cent. This material wasground so that approximately one-third passed through a 300-mesh screen.It was then compressed into pellets of the usual size and shape employedin catalytic operations. The pellets were immersed in an aqueoussolution of chromium tricxide. They were then removed from the solutionand heated at about 1000" F. for several hours to eiiect completeremoval of both free and combined water. The catalyst so preparedcontained 90 weight per cent alumina and 10 weight per cent chromia.

Normal butane was contacted, in a dehydrogenation system at 1100" F. anda space velocity of 500 gaseous volumes per volume of catalyst per hour,with the catalyst prepared as described above. The yield of normalbutenes plus butadiene per pass was approximately 40 per cent.

A second catalyst was prepared by a method which was identical to thatdescribed above with the exception that commercially available pelletsof activated alumina were substituted for the activated alumina preparedaccording to this invention. When the second catalyst was used in thenormal butane dehydrogenation system under the conditions previouslyspecified, the yield of normal butenes plus butadiene per pass was only32 per cent.

EXAlVIPLE II Alumina trihydrate, as in Example I, was partiallydehydrated by heating in a gas-fired rotary kiln. A weighed sample ofthe par-tially dehydrated alumina, when ignited to constant weight at2200 F., underwent a weight loss of approximately 23 per cent. Thepartially dehydrated alumina was then finely ground and was formed intopellets, which were subsequente ly heated at 1000 F. for 3 hours. Theactivated alumina pellets obtained by this procedure had a surface areaof 239.0 square meters per gram, determined by low-temperature gasadsorption.

The surface areas of two different samples of commercial activatedalumina pellets were measured by low-temperature gas adsorption. Thefirst had a surface area of only 161.5 square meters per gram; thesecond, an area of only 112 square meters per gram.

T. claim:

1. The improved method of dehydrogenating a. dehydrogenatablehydrocarbon to a less saturated hydrocarbon which comprises contactingsaid dehydrogenatable hydrocarbon under dehydrogenating conditions witha pelleted alumina catalyst prepared by the steps of calcining hydratedalumina containing at least 28 per cent of combined water underconditions such that the resulting material when ignited to constantweight at about 2200 F. undergoes a weight loss ranging from 20 to 26per cent, forming the resulting material into pellets, and calciningsaid pellets under such conditions as to remove residual water ofhydration, so as to dehydrogenate said dehydrogenatable hydrocarbon toa, less saturated hydrocarbon, and recovering the resulting hydrocarbon.

2. The improved method of dehydrogenating a parafiin to a correspondingless saturated aliphatic hydrocarbon which comprises contacting saidparaffin under dehydrogenating conditions with a pelleted aluminacatalyst prepared by the steps or calcining hydrated alumina containingat least 28 per cent of combined water under conditions such that theresulting material when ignited to constant Weight at about 2200 F.undergoes a weight loss ranging from 20 to 26 per cent, forming theresulting material into pellets, and calcining said pellets under suchconditions as to remove residual water of hydration, so as todehydrogenate said paramn to a corresponding less satuatcd aliphatichydrocarbon, and recovering the resulting hydrocarbon.

3. The improved method of dehydrogenating normal butane to normalbutenes and butadiene which comprises contacting said normal butaneunder dehydrogenating conditions with a pelleted alumina catalystprepared by the steps of calcining hydrated alumina containing at least28 per cent of combined water under conditions such that the resultingmaterial when ignited to constant weight at about 2200 F. undergoes aweight loss ranging from 20 to 26 per cent, forming the resultingmaterial into pellets, and calcining said pellets under such conditionsas to remove residual water of hydration, so as to dehydrogenate saidnormal butane; and recovering the resulting hydrocarbon.

4. The improved method of dehydrogenating an aliphatic hydrocarbon to acorresponding less saturated aliphatic hydrocarbon which comprisescontacting said aliphatic hydrocarbon under dehydrogenating conditionswith pelleted alumina having incorporated therein a dehydrogenationcatalyst, said pelleted alumina having been prepared by the steps ofcalcining hydrated alumina containing at least 28 weight per cent ofcombined water under such conditions that the resulting material whenignited to constant weight at about 2200 F. undergoes a weight loss inthe range of 20 to 26 per cent, finely grinding the resulting material,forming the resulting finely ground material into pellets, calciningsaid pellets under such conditions as to remove residual combined water,so as to dehydrogenate said hydrocarbon to a corresponding lesssaturated aliphatic hydrocarbon, and recovering the resultinghydrocarbon.

5. The process of claim 4 in which the dehydrogenation catalystincorporated in the alu mina is a metal oxide.

6. The process of claim 4 in which the dehyrogenation catalystincorporated in the alumina is chromium oxide.

7. The process of claim 4 in which the dehydrogenation catalystincorporated in the alumina is molybdenum oxide.

8. The process of claim 4 in which the dehydrogenation catalystincorporated in the alumina is vanadium oxide.

9. The improved method of dehydrogenating a paraifin to a correspondingless saturated aliphatic hydrocarbon which comprises contacting saidparafiin under dehydrogenating conditions with pelleted alumina havingincorporated therein a dehydrogenation catalyst, said pelleted aluminahaving been prepared by the steps of calcining hydrated aluminacontaining at least 28 weight per cent of combined water under suchconditions that the resulting material when ignited to constant weightat about 2200 F. undergoes a weight loss in the range of 20 to 26 percent, finely grinding the resulting material, forming the resultingfinely ground material into pellets, calcining said pellets under suchconditions as to remove residual combined water, so as to dehydrogenatesaid parafiin to a corresponding less saturated aliphatic hydrocarbon.and recovering the resulting hydrocarbon.

10. The process of claim 9 in which the dehydrogenation catalystincorporated in the alumina is a metal oxide.

11. The process of claim 9 in which the dehydrogenation catalystincorporated in the alumina is a chromium oxide.

12. The process of claim 9 in which the dehydrogenation catalystincorporated in the alumina is a molybdenum oxide.

13. The process of claim 9 in which the dehydrogenation catalystincorporated in the alumina is a vanadium oxide.

14. The improved method of dehydrogenating normal butane to normalbutenes and butadiene which comprises contacting normal butane underdehydrogenating conditions with pelleted alumina having incorporatedtherein a dehydrogenation catalyst, said pelleted alumina having beenprepared by the steps of calcining hydrated alumina containing at least28 per cent of combined water under such conditions that the resultingmaterial when ignited to constant weight at about 2200 F. undergoes aweight loss in the range of 20 to 26 per cent, finely grinding theresulting material, forming the resulting finely ground material intopellets, calcining said pellets under such conditions as to removeresidual combined water, so as to dehydrogenate normal butane, andrecovering the resulting hydrocarbon.

15. The process of claim 14 in which the dehydrogenation catalystincorporated in the alumina is a metal oxide.

16. The process of claim 14 in which the dehydrogenation catalystincorporated in the alumina is a chromium oxide.

17. The process of claim 14 in which the dehydrogenation catalystincorporated in the alumina is a molybdenum oxide.

18. The process of claim 14 in which the dehydrogenation catalystincorporated in the alumina is a vanadium oxide.

JAMES R. OWEN.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,868,869 Barnitt July 26, 1932 2,277,512 de Simo et a1 Mar.24, 1942 2,311,979 Corson et a1. Feb. 23, 1943 2,398,126 Thacker et al.Apr. 9, 1946 2,399,678 Houdry et al May 7, 1946 2,402,854 Thomas June25, 1946 2,469,420 Thacker May 10, 1949 2,487,563 Layng Nov. 8, 1949

1. THE IMPROVED METHOD OF DEHYDROGENATING A DEHYDROGENATABLE HYDROCARBON TO A LESS SATURATED HYDROCARBON WHICH COMPRISES CONTACTING SAID DEHYDROGENATABLE HYDROCARBON UNDER DEHYDROGENATING CONDITIONS WITH A PELLETED ALUMINA CATALYST PREPARED BY THE STEPS OF CALCINING HYDRATED ALUMINA CONTAINING AT LEAST 28 PER CENT OF COMBINED WATER UNDER CONDITIONS SUCH THAT THE RESULTING MATERIAL WHEN IGNITED TO CONSTANT WEIGHT AT ABOUT 2200* F. UNDERGOES A WEIGHT LOSS RANGING FROM 20 TO 26 PER CENT, FORMING THE RESULTING MATERIAL INTO PELLETS, AND CALCINING SAID PELLETS UNDER SUCH CONDITIONS AS TO REMOVE RESIDUAL WATER OF HYDRATION, SO AS TO DEHYDROGENATE SAID DEHYDROGENATABLE HYDROCARBON TO A LESS SATURATED HYDROCARBON, AND RECOVERING THE RESULTING HYDROCARBON. 